1. Field of the Invention
The present invention relates to a time division multiple access radio data communication method, and more particularly to a time division multiple access radio data communication method wherein radio communication channels are allocated fixedly to carry out multiple access data communication.
2. Description of the Related Art
Generally in a radio system in which multiple access communication is carried out, 1:N time division multiple communication is carried out between a single base station equipment and a plurality of out station equipment which face the base station equipment. In this instance, particularly where the system is of the type in which both telephone communication and data communication are involved, in the telephone communication, channel allocation control is carried out by a demand assign method wherein, only when a call is generated in the base station equipment or one of the out station equipment, a radio communication channel is allocated between the base station equipment and the out station equipment. On the other hand, in the data communication, channel allocation control is carried out by a pre-assignment method wherein a radio communication channel by which data communication is to be carried out is allocated fixedly in advance between a data terminal equipment connected to the base station equipment and another data terminal equipment connected to each out station equipment facing the base station equipment.
FIG. 1 is a view illustrating a conventional time division multiple access radio data communication method, and FIG. 1A is a block diagram showing a conventional example of a time division multiple access radio data communication system and FIG. 1B is a diagrammatic view illustrating a state of radio time slots of the conventional time division multiple access radio data communication system.
The conventional time division multiple access radio data communication method shown in FIG. 1A includes base station equipment 1, a plurality of data terminal equipment 1a, 1b and 1c connected to base station equipment 1, a plurality of out station equipment 10, 11 and 12 which face base station equipment 1 with radio, and data terminal equipment 10a, 11a and 12a connected to out station equipment 10, 11 and 12, respectively. In the downward from the base station equipment to the out station equipment, data communication is carried out by the TDM method, and in the upward from the out station equipment to the base station equipment, data communication is carried out by the TDMA method. Here, operation when data terminal equipment 1a and data terminal equipment 10a, data terminal equipment 1b and data terminal equipment 11a, and data terminal equipment 1c and data terminal equipment 12a carry out data communication in respective facing relationships between each other is described.
First, for the individual facing data terminal equipment, radio time slots to be used as radio communication channels are allocated fixedly in advance. That is, radio time slot TS0 is allocated fixedly to data terminal equipment 1a and data terminal equipment 10a, radio time slot TS1 is allocated fixedly to data terminal equipment 1b and data terminal equipment 11a, and radio time slot TS2 is allocated fixedly to data terminal equipment 1c and data terminal equipment 12a. Since radio time slots TS0, TS1 and TS2 are allocated at different positions which do not overlap with each other on a time basis as shown in FIG. 1B, data signals transmitted using those time slots do not interfere with each other at all. If a call is generated in any data terminal equipment in the system, then since different radio time slots are allocated to the different data terminal equipment, data communication can be carried out between the two facing data terminal equipment without fail.
In data transmission in the downward, data signals sent out from data terminal equipment 1a, data terminal equipment 1b and data terminal equipment 1c are inputted to base station equipment 1, by which they are multiplexed. Thereafter, the multiplexed data signals are transmitted to out station equipment 10, out station equipment 11 and out station equipment 12 using the TDM method. That is, the data signal from data terminal equipment 1a is multiplexed for radio time slot TS0, the data signal from data terminal equipment 1b is multiplexed for radio time slot TS1 and the data signal from data terminal equipment 1c is multiplexed for radio time slot TS2, and the thus multiplexed data signals are sent out to the respective individual out station equipment. It is to be noted that quite the same data signal is sent out from the base station equipment to the individual out station equipment. In each of the out station equipment, only a data signal addressed to the out station equipment itself is selectively demultiplexed and taken out, and the data signal is sent out to a data terminal equipment connected to the out station equipment. That is, the data signal multiplexed for radio time slot TS0 is demultiplexed by out station equipment 10 and sent out to data terminal equipment 10a, the data signal multiplexed for radio time slot TS1 is demultiplexed by out station equipment 11 and sent out to data terminal equipment 11a, and the data signal multiplexed for radio time slot TS2 is demultiplexed by out station equipment 12 and sent out to data terminal equipment 12a.
In data transmission in the upward, data signals from the data terminal equipment connected to the out station equipment are multiplexed for the radio time slots individually allocated thereto by the out station equipment, and sent out as burst signals to the base station equipment using the TDMA method. That is, the data signal from data terminal equipment 10a is inputted to out station equipment 10 and multiplexed for radio time slot TS0 and is sent as a burst signal to the base station equipment 1. Similarly, the data signal from data terminal equipment 11a is inputted to out station equipment 11 and multiplexed for radio time slot TS1 whereas the data signal from data terminal equipment 12a is inputted to out station equipment 12 and multiplexed for radio time slot TS2 and respective signals are sent as burst signals to base station equipment 1. In the base station equipment, the data signals from the individual out station equipment are individually demultiplexed and taken out, and the data signals are sent out to the individually corresponding data terminal equipment connected thereto. That is, the data signal multiplexed for radio time slot TS0 is sent out to data terminal equipment 1a, the data signal multiplexed for radio time slot TS1 is sent out to data terminal equipment 1b, and the data signal multiplexed for radio time slot TS2 is sent out to data terminal equipment 1c.
The operation described above is carried out, when data signals are sent out from the data terminal equipment, irrespective of whether or not such control signals as a request to send signal or a clear to send signal accompany them.
It is to be noted that, for convenience of description, in FIG. 1A, the number of out station equipment is 3 and the number of data terminal equipment connected to each out station equipment is 1, and those elements such as circuits and signals lines which are not particularly significant are omitted.
In the conventional time division multiple access radio data communication method described above, radio time slots to be used as radio communication channels are allocated fixedly in advance and used between individually facing data terminal equipment. Therefore, the conventional time division multiple access radio data communication method has a problem in that, where a plurality of data terminal equipment are included in a radio communication system, even when data communication is not actually being carried out with those data terminal equipment, a plurality of radio time slots are occupied, and particularly where the amount of data communication is low or the data transmission amount is small or else data communication is carried out only periodically or intermittently, the efficiencies of utilization of the radio time slots is low.
Further, the conventional time division multiple access radio data communication method has another problem in that, where the base station equipment requires a number of data terminal equipment and interface units therefore equal to the number of data terminal equipment connected to the individual out station equipment, and the structure of the system will become large.